> How would I generate these id/sequence values, either as a 
> second pass, or as part of the first pass which generates 
> this structure from the non-hierarchical source file?

> <root>
>     <a id="1">
>         <b id="2">
>             <e/>
>         </b>
>         <b id="3">
>             <c id="4"/>
>         </b>

I think the only way to do this is in a second pass. It then becomes fairly
easy:

Assuming you give the elements a blank id attribute in the first pass
(id=""), then in the second pass do

<xsl:template match="*[@id]" mode="pass2">
  <xsl:copy>
    <xsl:attribute name="id">
      <xsl:number level="any" count="*[@id]"/>
    </xsl:attribute>
    <xsl:apply-templates mode="pass2"/>
  </xsl:copy>
</xsl:template>

plus an identity template.

Michael Kay
http://www.saxonica.com/